1. Field of the Invention
The present invention is directed to a composite bearing structure. More particularly, the present invention is directed to a bearing structure having a bearing surface of alternating hard metal and soft metal areas which are metallurgically bonded to a base metal substrate. The present invention is also directed to a process for making the composite bearing structure.
2. Brief Description of the Prior Art
Bearings adapted for accommodating rotating or lineal motion are well known in the prior art and are practically ubiquitous in machines, engines and like mechanical devices.
Generally speaking, friction bearings incorporate two or more bearing surfaces which are in sliding motion relative to one another. These bearing surfaces optimally should have high load capacity, low friction, minimal wear and long useful life. As is well appreciated by those skilled in the art, the above-noted requirements are especially difficult to satisfy in bearings used in certain harsh environments such as in internal combustion engines and drilling machinery utilized "downhole", when prospecting for oil, gas or minerals.
In its efforts to meet the above-noted and other requirements, and especially for "downhole" and other "severe environment" applications, the prior art has provided bearing surfaces made of materials of very high hardness. Typically, these materials of high hardness are alloys of metal carbides, and are known in the art as "hardfacing" alloys of various proprietory names (such as STELLITE).
Alternatively, the prior art has provided bearing structures wherein one of the two adjacent, slidingly engaging bearing surfaces is made of a soft metal, such as copper, silver, or tin alloys. As still another alternative, the prior art has provided composite bearing surfaces which incorporate alternating soft and relatively hard metal areas exposed for sliding engagement with an adjacent bearing surface. Examples of bearing structures of the above noted and related composite construction, may be found in U.S. Pat. Nos. 3,961,104; 3,235,316; 2,971,248; 2,268,869 and 356,331.
More specifically, U.S. Pat. No. 3,235,316 discloses a composite bearing wherein appropriate recesses are machined into a suitable substrate. Inlays of an "anti-friction" or "anti-galling" soft metal compositon are placed into the recesses. The resulting composite bearing surface is said to have improved wear characteristics.
U.S. Pat. No. 2,971,248 discloses a composite bearing wherein a first metal alloy of relatively high load bearing capacity (such as aluminum alloy) is applied to a suitable backing strip or support. Recesses formed in the first metal alloy are mechanically inlaid with a second metal alloy (such as Babbit metal) having anti-seizure qualities.
U.S. Pat. No. 2,268,869 describes bearing structures wherein grooves or recesses machined into a base metal are filled with a mixture of an abrasive metal oxide and a suitable binder, such as sodium silicate. The resulting bearings are said to have improved load bearing capacity.
A principal disadvantage of the prior art composite bearing structures is that the grooves or recesses which accept the "second" material to form the composite, are mechanically placed or machined into the base or substrate metal. Understandably, machining the recesses into the substrate is costly, rendering the prior art composite bearings relatively uneconomical.
Another disadvantage of prior art composite bearing structures is that one of the materials of the composite bearing surface is necessarily the very material of the base or substrate. This disadvantage inherently flows from the hitherto known methds for fabricating the composite bearings. Thus, the hitherto known composite bearings fail to take advantage of specialized hardfacing alloy compositions which are available in the art to provide extra hard, thin surfaces on less expensive metal based substrates.
The present invention is designed to overcome the problems experienced in the prior art regarding high costs of composite bearings, and to provide for the first time, a composite bearing which utilizes specialized hardfacing alloys in conjunction with soft metals to provide an improved bearing surface.